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Introduction
Ernest Sternglass: Radiation Relatively More Harmful at Low Levels Alice Stewart: Total Risk of Radiation Exposure Underestimated |
Introduction
This publication discusses the question of whether there is an increased risk for developing cancer among people who were exposed to radiation released from Hanford. It offers the opinions of three scientists: Drs. Ernest J. Sternglass, Alice M. Stewart and Gregg S. Wilkinson. Their essays follow in alphabetical order.
In your opinion, what kind of dose range from Hanford could have posed a public health risk by causing cancer?
Comment specifically on the various nuclides for which doses will be calculated by the Hanford Environmental Dose Reconstruction Project.
Each scientist has approved the edited version of their essay and selected
references follow each piece. A complete bibliography of all the references used by the
three scientists is available from the Network.
ERNEST J. STERNGLASS, Ph.D. has been Professor Emeritus of Radiology at the University of Pittsburgh's School of Medicine since 1983. He has held professorships in radiology and physics at several universities, including Stanford, Indiana University, and the Institute Henri Poincare in Paris, France. Dr. Sternglass was the Director of the Apollo Lunar Scientific Station Program while at Westinghouse Research Laboratories. His doctorate in Engineering Physics (1953) comes from Cornell University, as does his post-graduate and undergraduate degrees in Engineering Physics and Electrical Engineering, respectively. He taught physics at George Washington University and held a research fellowship at Cornell University. Dr. Sternglass has received many academic and professional honors, is a member of several professional societies and holds 13 patents. He is the author of several books on low-level radiation.
Exposure to radioactive substances, such as those released from Hanford, increases the risk of cancer. There is increasing evidence that the risk of cancer is proportionately greater at low doses. These low doses are only a thousandth of the dose levels of the Japanese atomic bomb survivors. The atomic bombs exposed the Japanese to short bursts of external radiation.
Internal radiation doses from contaminated food and water over a long time appear to damage the body much more than the same doses from short external exposures, such as X-rays. Around Hanford, people received internal exposure over a long time.
Highly toxic forms of oxygen, called free radicals, can increase the harmfulness of radiation exposure. The power of free radicals to do harm increases as the dose levels decrease. The lower the dose per year, the higher the risk. The increasing harmfulness of free radicals has been found down to levels of 20-200 millirem per year. This level of exposure is equal to the amount received from background radiation.
This evidence shows that constant, low levels of radiation are relatively more harmful than higher levels of exposure over a short time. This is especially important for people who were exposed to the radiation releases from Hanford.
Selected References
Gould, J.M., E.J. Sternglass, "Nuclear Fallout, Low Birthweight, and Immune Deficiency." International Journal of Health Services: 1994; 24 (2): 311-335.
Mangano, J.J. "Cancer Mortality Near Oak Ridge, Tennessee." International
Journal of Health Services: 1994; 24 (3).
ALICE M. STEWART, M.D., has been a Senior Research Fellow at Birmingham University in England since 1974, where her work continues on the Oxford Survey of Childhood Cancers. This study began over 30 years ago while she was pursuing her career in scientific research in social medicine at Oxford University. Her epidemiological findings while at Oxford linked the use of pre-natal X-rays to childhood leukemias. She continues to speak out against the risks of low-dose radiation exposure to workers in the nuclear industry. Dr. Stewart was a founding member of both the International Epidemiological Society and the Society for Medicine. She received her medical degree from Cambridge University in 1932 and was the youngest woman to be elected to the British Royal College of Physicians before 1947. She continues to study the health of workers in U.S. nuclear weapons facilities.
Exposure to radiation can harm the immune system. A weakened immune system can result in an exposed person catching an infection and possibly dying from it or any infection-related cause of death. Such a person might also have developed a cancer from the radiation exposure. But because the person died from another illness first, the cancer did not have time to fully develop and be diagnosed. By not accounting for deaths from weakened immune systems, current risks of cancer deaths from radiation exposure underestimate the harmfulness of radiation.
It is unlikely that the harmfulness of radiation is reduced at low-dose levels. Rather, it is possible that the mutations to cells caused by repeated and unavoidable exposures to background radiation are the most common cause of cancer. In addition, a large British study of childhood cancer deaths (Oxford Survey of Childhood Cancers) has found many reasons why detection of cancers caused by constant low-level radiation is always a complex problem.
According to data from the Oxford Survey, childhood cancers include a relatively large number of embryomas, cancers of the embryo. These may be the result of exposure while in the womb to background radiation, as well as medical X-rays. Furthermore, for all cancers that began in the womb, there was evidence of mounting sensitivity to infections while the cancers were growing. Consequently, deaths during the latency period (the time it takes for cancers to develop) of a childhood cancer are common. The latency period deaths also result in falsely low rates of leukemia and lymphoma for children who have survived high rates of infant mortality. Leukemia and lymphoma are cancers of white blood cells.
Besides causing early cancer deaths, infections can also shorten the latency period. In countries with low rates of infant mortality, cases of leukemia and lymphoma are relatively common. However, these cases are distributed unevenly: there are higher rates in rural areas and in people who are well-to-do.
According to the Oxford Survey, immunizations against infectious diseases have reduced the risk of an early cancer death. However, African children who live in areas of holoendemic malaria and have survived a high risk of dying during infancy rarely develop leukemia. Therefore, it is possible that, even in children, the spread of cancer cells can be prevented by immune system reactions to the dangerous situations created by the malarial parasite. Based on this evidence, the number of cancers depends less upon the level of exposure to background radiation than upon the nature and intensity of indigenous infections. In addition, the number of cancers depends on such things as levels of family income, population density and the availability of immunizations.
The only measurable effect of the Hanford releases could be the one caused by the releases of iodine-131. By its effect on the thyroid gland, these releases would increase the risk of cancers that are normally rare. Thyroid cancers accounted for only three of the 22,351 cancers eventually included in the Oxford Survey. Therefore, even a single case of thyroid cancer among persons exposed (in the womb or as young children) to the iodine releases from Hanford would be a highly suspicious finding.
Evidence of a special association between radioactive iodine and thyroid cancers has already been obtained from Marshall Islanders and Ukrainian children. Therefore, I recommend that a study identify all live births for the period of 1944-1955 in the regions covered by the Hanford Environmental Dose Reconstruction Project, as well as all cancer deaths in this population. This relatively simple procedure would detect any thyroid cancer effect of the reconstructed doses. Remember, even one case of thyroid cancer would be highly suspicious. Comparing the thyroid cancer effect to other populations and other cancers could be done to estimate the overall effect of all the Hanford releases.
Selected References
Bithell, J.F., A.M. Stewart, "Pre-Natal Irradiation and Childhood Malignancy: A Review of British Data from the Oxford Survey." British Journal of Cancer: 1975; 31: 271-287.
Gilman, E.A., G.W. Kneale, E.G. Knox, A.M. Stewart, "Pregnancy X-rays and Childhood Cancers: Effects of Exposure Age and Radiation Dose." Journal of the Society for Radiological Protection: 1988; 8 (1): 3-8.
Kneale, G.W., A.M. Stewart, L.M. Kinnier Wilson, "Immunizations Against Infectious Diseases and Childhood Cancers." Cancer Immunology and Immunotherapy: 1986; 21: 129-132.
Stewart, A.M., G.W. Kneale, "The Immune System and Cancers of Fetal Origin." Cancer Immunology and Immunotherapy: 1982; 14: 110-116.
Stewart, A.M., J. Webb, D. Giles, D. Hewitt, "Malignant Diseases in Childhood and
Diagnostic Irradiation In Utero." The Lancet: 1956; ii: 447.
Gregg S. Wilkinson, M.A., Ph.D. is a Professor of Epidemiology in the Department of Preventive Medicine and Community Health, and Director of the Division of Epidemiology and Biostatistics at the University of Texas Medical Branch (UTMB) in Galveston, Texas. Prior to joining the faculty at UTMB, Dr. Wilkinson was an Associate Epidemiologist with Epidemiology Resources, Inc., and he also served as the Principal Investigator for the nationwide study of U.S. plutonium workers at the Los Alamos National Laboratory. He received his doctorate in 1973 from the State University of New York at Buffalo and held a post-doctoral fellowship at Duke University Medical Center. In addition to his research concerning low- dose effects from ionizing radiation, Dr. Wilkinson's research interests include the epidemiology of neural tube and other birth defects, environmental and occupational epidemiology and epidemiological methods.
At what levels of exposure to radioactive materials is there an increased risk of cancer? Two factors must be known before that question can be answered. First, information on exposures (or doses) to individual members of the population under consideration must be calculated. Second, health problems that the population experienced after the exposure must be identified. From this information, a risk estimate can be made.
Regarding the list of radioactive materials for which doses are being calculated, I am limiting my comments to the radioactive elements with which I have some experience: plutonium-239 and iodine-131.
Plutonium-239
Plutonium causes cancer in animals. One human study suggested that Rocky Flats workers who had plutonium uptakes of more than two nanocuries had increased risks of dying (Wilkinson 1987). A similar study of Hanford workers, however, found no increased risks (Gilbert 1989). Unfortunately, the Hanford study had little chance of detecting anything other than huge increases in risk. This was due to the relatively small number of exposed workers and the skewed nature of the exposures. There were few workers with recorded body burdens greater than 5% of the maximum permissible body burden (2 nanocuries). The U.S. Department of Energy sets the standard for the maximum permissible body burden at 40 nanocuries of plutonium.
Generally, workers experience higher exposures to plutonium than the public. Thus, doses for the population exposed to the Hanford releases are probably not high enough to result in detectable increases in disease rates. This does not mean that there is no increase in risk. Rather, it is very difficult to detect anything other than very large increases in risk. This is due to the limitations of existing information and the methods that epidemiologists have available to them.
Most studies that have measured plutonium uptake by the potentially exposed public have been inconclusive or have not found increased levels of plutonium in human tissues that could be attributed to the operations of weapons facilities (Cobb 1982, Nelson 1993). Unfortunately, in recent years the emphasis of programs that were monitoring the amount of plutonium taken up by the public and by workers has shifted almost exclusively to only monitoring nuclear workers (Nelson 1993).
Iodine-131
Potential risks associated with iodine-131 are a serious concern. Researchers have found an increased rate of thyroid growths in people who were exposed as children. Their doses were as low as nine rads (Ron 1989). The thyroid easily absorbs iodine-131 through the food chain. Scientists have recently identified an increased thyroid cancer incidence among people in Los Alamos County, New Mexico. No one has begun a comprehensive dose reconstruction at Los Alamos. The sustained high level of thyroid cancer in a population living near that nuclear weapons plant is cause for concern.
There is a low chance of dying from thyroid cancer because it can be successfully treated. Because of this, researchers should study cancer incidence rather than cancer deaths to determine if increased risks of thyroid cancer are present. A further complication in determining risk is that many tumor registries do not collect information on benign growths or other types of illnesses. Studies show that there is also an increase in benign growths among radiation-exposed individuals. Other thyroid abnormalities may be present. Thus, the sum of thyroid problems which may be due to iodine-131 exposure will be difficult to determine.
Conclusion
A valid estimate of the health risk posed by Hanford releases will require accurate individual dose estimates, accurate measures of disease incidence and at least a moderate number of affected individuals. Risk estimates may only be possible for thyroid disease from exposure to iodine-131. For other health problems and for other radioactive materials, valid estimates of disease rates and exposure levels are unlikely. Because exposures from Hanford are unique, comparisons with other exposures, other health problems or animal studies may be of limited value and often misleading.
Selected References
Cobb, J.C., B.C. Eversole, P.G. Archer, et al. "Plutonium Burdens in People Living Around the Rocky Flats Plant." Final Report submitted to Environmental Monitoring Systems Laboratory, U.S. Environmental Protection Agency, P.O. Box 15027, Las Vegas, NV 89114. June 1982.
Gilbert, E.S., G.R. Petersen, J.A. Buchanan, "Mortality of Workers at the Hanford Site: 1945-1981." Health Physics: 1989; 56:11-25.
Nelson, I.C., V.W. Thomas, R.L. Kathren, "Plutonium in South-Central Washington State Autopsy Tissue Samples: 1970-1975." Health Physics: 1993; 64 (4): 422-428.
Ron, E., B. Modan, D. Preston, et al. "Thyroid Neoplasia Following Low-Dose Radiation in Childhood." Radiation Research: 1989; 120: 516-531.
Wilkinson, G.S., G.L. Tietjen, L.D. Wiggs, et al. Mortality Among Plutonium and Other Radiation Workers at a Plutonium Weapons Facility. American Journal of Epidemiology: 1987; 125: 231-250.